This invention relates to a process for treating waste water from industrial sources. In a more specific aspect, this invention relates to a process for treating waste water having a relatively high chemical oxygen demand (COD) caused by organic material which is predominantly soluble in water.
It is well known in the art to use a biochemical treatment step for treating municipal sewage. Use of biochemical treatment is also known for waste water from chemical plants as evidenced by Hudson, Jr. et al, U.S. Pat. No. 3,646,239.
Waste water from chemical plants generally differs substantially from municipal sewage in that it contains a higher concentration of organic matter and, in addition, this organic matter is predominantly soluble whereas in municipal sewage the organic matter is predominantly solids. The high concentration of organic matter in waste water from chemical processes makes the treatment of this water extremely difficult. For instance, in a municipal sewer plant, chemical oxygen demand may be no more than 300 to 400 milligrams per liter and a 90 percent reduction leaves the effluent within generally accepted standards, whereas with waste water from a chemical plant which may have a chemical oxygen demand of 2500 or more, a 90 percent reduction leaves the effluent still unsuitable for disposal in view of current Federal specifications requiring waste water to have a maximum COD of approximately 200 and a maximum BOD (biological oxygen demand) of approximately 20 before discharge into a river or pond.
Accordingly, when high COD industrial wastes are to be treated, it is frequently necessary to supplement biotreating with another process such as chemical treatment, stripping, or adsorption.
Another problem encountered in biotreating industrial wastes is that these wastes may contain chemicals which are toxic to the microorganisms. The presence of such substances retards the activity of the microorganisms and reduces their population. The result is gradually poorer biotreater performance and unacceptable BOD and COD levels in the effluent. Known methods for overcoming the problem include (1) identification and elimination of the toxins, (2) dilution of the biotreater feed to lower toxin concentration to an acceptable level, and (3) pretreating the feed in some manner such as by carbon adsorption. These methods, however, have serious disadvantages. The first may be too expensive and it may be virtually impossible to identify and eliminate the toxins; the second is also costly and may be unacceptable to Government authorities since it increases the volume of the waste stream; and the third, while effective, is also costly in that the carbon beds become loaded rather rapidly, necessitating frequent regeneration and makeup of carbon. The use of carbon to "polish" all of the final effluent prior to discharge is also known, but this can be even more expensive than the use of carbon to pretreat waste water.